Joint compound and method of using same

ABSTRACT

A joint compound includes water, calcium carbonate, and a water-soluble polymeric set retarder formed from a monomer having two or more carboxyl groups. The joint compound is useful in various applications and in a hybrid joint compound made with a calcium sulfate hemihydrate setting-type joint compound.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 09/838,462filed Apr. 19, 2001, now U.S. Pat. No. 6,436,185 which is anon-provisional application of U.S. Provisional Patent Application Ser.No. 60/199,860 filed Apr. 26, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention generally relates to the production of cementitiouscompositions and, more specifically, the invention relates to theproduction of compounds for use in filling and coating joints betweenadjacent gypsum wallboard sheets, for repairing other imperfections inbuilding materials, and for texturizing.

2. Brief Description of Related Technology

A common manner of constructing interior walls includes the use ofinorganic wallboard panels or sheets such as gypsum wallboard, oftenreferred to simply as “wallboard” or “drywall.” Wallboard is typicallyproduced by enclosing a core of an aqueous slurry of gypsum and otheradditives between two large sheets of paper. After the gypsum slurry hasset and dried, the sheet is cut into standard sizes.

A wall is generally made by securing, e.g., with screws and/or nails,the wallboard to a support structure, for example vertically orhorizontalIy-oriented pieces of wood. Because wallboard istypically.supplied in standard-sized sheets or panels, when forming awall from the sheets there will generally be a number of joints betweenadjacent sheets. In most wallboard construction, it is necessary toconceal these joints between adjacent panels so that the wall will havea smooth, monolithic finish similar to that obtained with conventionalwet plaster methods. It is also typically necessary to conceal thescrews and/or nails used to secure the wallboard panels to framing, theindentations caused by the screws and/or nails, imperfections in thewallboard panels, and other materials (e.g., comer beads) used to formthe wall.

A number of joint compound compositions (sometimes referred to byapplicators as “mud”) that can be used to conceal the joints betweenadjacent sheets of wallboard, other imperfections in the wallboard, andother construction points (e.g., comer beads) are known.

To conceal the joints between wallboard panels, a joint compound istypically applied in several layers or coats. A first coat of jointcompound is placed in the joint between the wallboards with a wallboardknife, blade, or trowel. The first coat is primarily for the purpose offilling the space between the adjacent wallboards. Joint tape (forexample, made of paper) can then be embedded into the first coat ofjoint compound. The joint compound may be applied in several, e.g.,three, coats or layers in order to obtain a smooth finish. Each coat ofjoint compound must be allowed to dry or set prior to the placement ofthe next coat of joint compound. (If the prior coat is not allowed todry or set, problems such as excess shrinkage and/or cracking canoccur.) Once dry or set, the treated area is sanded before applying thenext finishing coat of joint compound.

Joint compounds can be used for other purposes, for example, to repairimperfections in various building materials and for adding texture towalls and ceilings.

There are many different types of joint compounds: Joint compounds canbe supplied in a dry powder form or in a mill-mixed, ready-mix form.They can also be of a “drying” type or a setting type.

The joint compound can be supplied in the form of a dry powder, to whichan amount of water is added at the work site by the applicators to givethe joint compound a suitable consistency. Other joint compounds, oftenreferred to as “ready-mix” or “ready-mixed” joint compounds, arepre-mixed with water and other additives during manufacturing theproduct. These joint compounds are generally packaged and sold in acorrugated box or plastic pail in a form that is suitable for use withlittle or no addition of water at the job site.

Among the prior art joint compound compositions, it is generally knownto use a filler (e.g., calcium carbonate, calcium sulfate hemihydrate,or calcium sulfate dihydrate), thickener, preservative, and a binder, aswell as various other additives to produce a joint compound, asdisclosed in U.S. Pat. No. 5,653,797 (Aug. 5, 1997), the disclosure ofwhich is hereby incorporated herein by reference.

Many joint compounds are of the “drying” or “setting report” type.Drying-type joint compounds contain calcium carbonate (CaCO₃; i.e.,limestone) and/or calcium sulfate dihydrate (CaSO₄.2H₂0) and/or talc(Mg₃Si₄O₁₀(OH)₂ or 3MgO.4SiO₂.H₂O). Prior to use (generally duringmanufacturing), these components and a binder (along with several otheringredients) are mixed for a specific time with water. The drying-typejoint compound thus produced has a high ionic content and basic pH.After application, when the compound dries (i.e., water evaporates), adry, relatively hard cementitious material remains. The calcium sulfatedihydrate and calcium carbonate may comprise a substantial portion ofwhat is sometimes referred to as the filler component.

Many conventional drying-type joint compounds undergo shrinkage upondrying, which makes it difficult to achieve a smooth wall surface.Shrinkage can be particularly troublesome when a.second coat of compoundis applied over a previous coat that is not completely dried.

General ranges of ingredients used in an all purpose,conventional-weight, drying-type joint compound include the ingredientsshown in Table 1, below.

TABLE 1 CONVENTIONAL WEIGHT JOINT COMPOUND Ingredient Weight PercentageWater 20-37 Preservatives 0.02-1.0  Calcium Carbonate  10-100 Mica(Filler) 0.5-5.0 Attapulgite Clay (non-leveling agent) 0.5-5.0 CelluloseThickener 0.12-1.0  Latex (Binder) 1.0-4.0

To avoid various disadvantages of the drying-type of joint compound,compounds of the “setting type” have been developed. A setting-typejoint compound generally includes calcium sulfate hemihydrate(CaSO₄.½H₂O, also referred to as calcined gypsum). (See U.S. Pat. No.5,653,797.) To produce calcined gypsum, calcium sulfate dihydrate isconverted from raw gypsum to the hemihydrate state via a suitablecalcination process. A gypsum calcination process removes one andone-half molecules of water from each calcium sulfate dehydrate gypsummolecule. The hemihydrate form of calcium sulfate is substantially moresoluble in water than the dihydrate form of calcium sulfate. The calciumsulfate hemihydrate may comprise a substantial portion of what issometimes referred to as the filler component in a setting-type jointcompound.

During use in a setting-type joint compound, the calcium sulfatehemihydrate is rehydrated to the dihydrate state via the addition ofwater. This rehydration process normally takes place over a fairly shortperiod of time. Accordingly, it has been extremely difficult to producea setting-type joint compound comprising hemihydrate gypsum pre-mixedwith water, because the product would set in its storage container.Thus,joint compounds of the setting- type have generally had to besupplied in the powder form.

Ready-mixed, setting-type joint compounds are also known. For example,Jakacki et al. U.S. Pat. No. 4,661,161 (Apr. 28, 1987) discloses asetting-type joint compound comprising an aqueous slurry of calciumsulfate hemihydrate and a set retarding agent formed of two ingredients:an organic, proteinaceous retarder and a chelating agent, e.g., selectedfrom diethylene triamine pentaacetic acid, ethylene diamine tetraaceticacid, and salts thereof. This patent discloses that the compound has anadequately long shelf life for commercialization, and that when mixedwith an accelerator that the joint compound hydrates after a period oftime to form a set material having acceptable joint compound properties.However, it is believed that joint compounds of the setting, ready-mixtype have not been successfully commercially employed due to the need tofind a suitable retarding agent and a suitable accelerator to overcomethe retarding agent.

Setting-type joint compounds have the advantage of having generallyquicker finishing times (setting time) than drying-type joint compounds.This is advantageous for the reasons stated above. Further, becausesetting joint compounds form a crystalline network upon setting (asopposed to merely drying), these compounds typically provide a strong,more durable bond between adjacent wallboard sheets than do drying-typejoint compounds. However, because these compounds provide a strongcrystalline network upon setting, the joint compound is often harder tosand to a smooth finish.

A calcium sulfate hemihydrate-based, setting-type joint compound can becombined with a calcium carbonate-based, drying-type joint compound toproduce a joint compound having advantages of each individual type ofcompound. Such a hybrid joint compound can be used in applicationstypical of conventional drying-type and setting-type joint compounds.

One problem with this practice is that calcium carbonate acts as acalcium sulfate hemihydrate set accelerator. Thus, when a calciumsulfate hemihydrate-based, setting-type joint compound would, on itsown, set in a time frame of about 210 minutes, its set time after havingbeen mixed with a limestone-based drying-type joint compound (⅔ ofhybrid joint compound by volume) is substantially reduced, to about 60minutes. This drastic reduction in set time narrows in an unacceptablemanner the working time window for finishers in the field to apply thecompound.

One solution would seem to be the addition of a conventional setretarder to the drying-type joint compound. Others have disclosedretarding agents for use in certain other applications. However,although various types of retarders have been suggested, the purpose ofthe retarders, the final product, and the conditions under which theproduct is used (e.g., in wallboard manufacturing or cementing of pipesand casings of oil and gas wells) have differed substantially from thepurpose, production conditions, and working conditions of jointcompounds, particularly calcium carbonate-based, drying-type jointcompounds.

For example, although wallboard manufacturers have used certain types ofretarding agents, the purpose in that application is to prevent theimmediate absorption of water and stiffening of the slurry duringproduction, as well as to facilitate control of the slurry. In wallboardproduction, retarding agents are added to stabilize a stucco slurry foronly a matter of seconds. It is understood that retarding agents aretypically used in wallboard production at an extremely low rate, forexample at about 0.0007 weight percent (e.g., in a 1400 pound batch,about 30 grams of retarder could typically be added).

When left in an aqueous, high ionic content, basic pH slurry system madeup of such fillers as calcium carbonate and talc, conventional retarderscompletely lose their retarding potency towards calcium sulfatehemihydrate fairly rapidly, for example in as short as one day.

Accordingly, it would be desirable to provide a hybrid drying-type/setting-type joint compound that produces a strong durable bondbetween adjacent wallboard sheets and has reduced shrinkage, and yet isable to be sanded to a smooth finish like a drying-type joint compound.It would also be desirable to provide a ready-mixed, drying-type jointcompound that reduces the accelerating effect of calcium carbonatetowards the setting of calcium sulfate hemihydrate, and preferably whichis also storage stable for periods required for practical and commercialuse. Moreover, it would be advantageous to provide a method of producinga hybrid drying-type/setting-type joint compound that sets and/or driesin a time frame acceptable for practical and commercial use.

SUMMARY OF THE INVENTION

It is an objective of the invention to overcome one or more of theproblems described above.

Accordingly, one aspect of the invention is a drying-type joint compoundincluding water, calcium carbonate, and a water-soluble polymeric setretarder formed from a monomer having two or more carboxyl groups.

One embodiment of the invention provides a hybriddrying-type/setting-type joint compound including water, calciumcarbonate, calcium sulfate hemihydrate, and a water-soluble polymericset retarder formed from a monomer having two or more carboxyl groups.

Another embodiment of the invention provides a method of producing ahybrid drying-type/setting-type joint including the steps of forming amixture of calcium carbonate and a water-soluble polymeric set retarderformed from a monomer having two or more carboxyl groups, forming amixture of calcium sulfate hemihydrate and water, and combining theaforesaid mixtures.

Further aspects and advantages of the invention may become apparent tothose skilled in the art from a review of the following detaileddescription, taken in conjunction with the appended claims. While theinvention is susceptible of embodiments in various forms, describedhereinafter are specific embodiments of the invention with theunderstanding that the disclosure is illustrative, and is not intendedto limit the invention to the specific embodiments described herein.

DETAILED DESCRIPTION OF THE INVENTION

Generally, the invention is directed to joint compounds and methods ofproduction thereof.

One aspect of the invention is a drying-type joint compound. Adrying-type joint compound of the invention includes water, calciumcarbonate (limestone), and a water-soluble polymeric set retarder (setinhibitor) formed from a monomer having two or more carboxyl groups.

The amount of water used in a drying-type joint compound of theinvention can be from about 20 wt. % to about 37 wt. %, and ispreferably in a range of about 25 wt. % to about 35 wt. %, and morepreferably about 30 wt. % to about 33 wt. %, based on total weight ofjoint compound.

Calcium carbonate (limestone) may be purchased from Georgia Marble ofKennesaw, Ga., York Limestone of York, Pa., or Pfizer Limestone of NewYork, N.Y., for example. The calcium carbonate in a drying-type jointcompound of the invention is preferably at least 50 weight percent (wt.%) and more preferably about 60 wt. % to about 70 wt. %, of the totalweight of the joint compound.

Generally, a water-soluble polymeric set retarder used in thedrying-type joint compound of the invention is formed from a monomerhaving two or more carboxyl groups. The term “water-soluble” is definedherein to mean a minimum solubility of 5% by weight in water at 25 ° C.The monomer can be, for example, a dicarboxylic acid, such as adipicacid, phthalic acid, sebacic acid, and maleic acid, and a derivative ofa dicarboxylic acid (e.g., 2-methyl maleic acid, maleic anhydride, andester derivatives). The monomer can also be a higher order carboxylicacid, and a derivative of a higher order carboxylic acid (including oneor more of an anhydride and an ester). The monomer can also be a mixtureof any of the foregoing named compounds.

Preferably, the monomer is an unsaturated dicarboxylic acid or aderivative of an unsaturated dicarboxylic acid (including one or more ofan anhydride and an ester). More preferably, the monomer is selectedfrom the group consisting of maleic acid, derivatives of maleic acid,and mixtures thereof. Most preferably, the monomer is selected from thegroup consisting of maleic anhydride, maleic acid, and mixtures thereof.

The water-soluble polymeric set retarder used in the drying-type jointcompound of the invention can also be a salt of any of the foregoingnamed compounds and mixtures. Suitable salts include alkali metal salts,alkaline-earth metal salts, and ammonium salts. Sodium salts arepreferred.

When an acid anhydride such as maleic anhydride is used as the monomer,it can be subsequently hydrolyzed to a carboxylic acid, either beforeadding it to calcium carbonate and water to form a drying-type jointcompound of the invention, or in situ in the drying-type joint compoundof the invention.

Another preferred monomer (and a preferred polymeric set retarder)includes two or more carboxyl groups on successive carbon atoms, thesuccessive carbon atoms forming (becoming part of) the polymer backbone(chain). Stated another way, a preferred monomer includes at least twosuccessive carbon atoms that form (become part of) the polymer chain,and includes at least two carboxyl groups on the successive carbon atoms(i.e., depend from the successive carbon atoms). Maleic acid andsuitable derivatives of maleic acid are examples of this type ofpreferred monomer. In the case of maleic acid, the carboxyl groupsdepend directly from two successive carbon atoms, i.e., are bounddirectly to two successive carbon atoms, though this need not be thecase. For example, one or more of the carboxyl groups can be separatedfrom the corresponding successive carbon atom by one or more additionalatoms, preferably a saturated or unsaturated C₁-C₄ moiety.

Generally, monomers in which the carboxyl groups are located on themolecule closer to the carbon atoms that form the polymer backbone arepreferred. Likewise, polymeric set retarders in which the carboxylgroups are located on the polymer closer to the carbon atoms that formthe polymer backbone are preferred.

Preferably, a monomer moiety has a pK₁ less than about 4.26, morepreferably less than about 1.91. The lower a pK value (for example,pK₁), the greater the tendency of a carboxyl group (for example, thefirst carboxyl group) to dissociate and, by extension, the better itschances of interfering with gypsum crystal formation and growth.

The polymeric set retarder used in the drying-type joint compound of theinvention can be a homopolymer or a copolymer. The term copolymer isdefined herein to include terpolymers and higher order polymers.Copolymers are preferred, for reasons described below.

The polymeric set retarder used in the drying-type joint compound of theinvention preferably has a molecular weight sufficiently low such thatthe set retarder does not over-thicken the drying-type joint compound ofthe invention into which it is incorporated. Preferably, the molecularweight of the polymeric set retarder is from about 1,000 to about15,000, more preferably about 2,000 to about 5,000, most preferablyabout 3,000.

When using lower molecular weight monomers having two or more carboxylgroups (e.g., maleic acid), it is preferred to form a copolymer with oneor more other monomers. Without intending to be bound by any particulartheory, it is believed that it sometimes can be difficult to synthesizea homopolymer with a molecular weight as high as 3,000 using alow-molecular weight monomer such as maleic acid. Acrylates areparticularly preferred monomers for forming copolymers with lowermolecular weight monomers having two or more carboxyl groups, such asmaleic acid or maleic anhydride.

Other suitable monomers for copolymerization with a monomer having twoor more carboxyl groups include styrene, vinyl chloride, vinyl esters,acrylonitrile, acrylic acid, acrylate esters (e.g., methyl acrylate,ethyl acrylate, and n-butyl acrylate), salts of acrylic acid, salts ofacrylate esters, acrylamide, acrolein, vinylsulfonic acid, allylacetate, and alkenes such as ethylene, vinyl ketones, and carbonmonoxide. Salts of the foregoing monomers may also be useful,particularly alkali metal salts; sodium salts are particularlypreferred. Non-polar monomers (e.g., styrene, alkenes, etc.) arepreferably added in such a way that they do not detrimentally affect theoverall solubility of the resulting polymeric set retarder in aqueoussystems. Copolymers may be assembled by any suitable method, in randomor alternating additions, including by grafting a monomer having two ormore carboxyl groups onto existing polymers, and by condensations.

The amount of monomer having two or more carboxyl groups within acopolymer preferably ranges from about 10% to about 90%, most preferablyabout 50%. In a higher molecular weight polymeric set retarder, theamount of monomer having two or more carboxyl groups may be lower,whereas in a lower molecular weight polymeric set retarder, the amountof monomer having two or more carboxyl groups may be higher. In apreferred drying-type joint compound of the invention, the amount ofmonomer having two or more carboxyl groups is about 50% and themolecular weight is about 3,000.

A preferred compound useful as a polymeric set retarder in thedrying-type joint compound of the invention is sold under the trade nameALCOSPERSE 408 by Alco Chemical, a division of National Starch andChemical Company. This polymeric set retarder is a sodium saltterpolymer of maleic acid, acrylic acid, and a third non-ionic oranionic monomer. Maleic anhydride is reported to make up over 50% of therepeating units within the polymer chain. ALCOSPERSE 408 terpolymer isreported to have a weight average molecular weight of about 3,000, andis marketed as a 43% aqueous solution.

The amount of polymeric set retarder used in the drying-type jointcompound of the invention will vary depending on the particularapplication in which it is used. For example, when adding a drying-typejoint compound of the invention to a setting-type joint compound havinga relatively short set time, the amount of polymeric set retarder usedin the drying-type joint compound of the invention will be greater.Likewise, when adding a greater proportion of a drying-type jointcompound of the invention to a setting-type joint compound, the amountof polymeric set retarder used in the drying-type joint compound of theinvention can be reduced. Generally, the polymeric set retarder can beabout 0.001 wt. % to about 0.5 wt. %, preferably about 0.01 wt. % toabout 0.1 wt. % of the drying-type joint compound, based on the totalweight of the drying type joint compound.

Thus, for example, when adding about two parts by volume of adrying-type joint compound of the invention to one part by volume of asetting-type joint compound having a set time of about 210 minutes, thepolymeric set retarder preferably is about 0.03 wt. % to about 0.08 wt.%, most preferably 0.04 wt. % of the drying-type joint compound, basedon the total weight of the drying-type joint compound, to achieve a settime of about 80 to about 150 minutes, preferably about 120 minutes.

In a drying-type joint compound of the invention the amount of polymericset retarder is preferably increased with increasing calcium carbonatecontent. Likewise, in a drying-type joint compound of the invention theamount of polymeric set retarder is preferably decreased with decreasingcalcium carbonate content.

Optional ingredients in the drying-type joint compound of the inventioninclude clay, mica, talc, binders, fillers, thickening agents,preservatives, defoaming agents, gypsum, latex, glycol, humectants, andother ingredients suitable for use in joint compounds.

The drying-type joint compound of the invention is generally produced bycombining both solid and liquid ingredients. The solid ingredients usedin the drying-type joint compound of the invention, described in greaterdetail below, can include limestone, perlite, clay, mica, thickeners,binders, talc, gypsum (calcium sulfate dihydrate), and urea. Two or moreof the solid materials or ingredients can be pre-blended in a mixingapparatus or blender. The solid materials may include absorbed orchemically combined moisture.

The liquid ingredients used in the drying-type joint compound of theinvention are also preferably pre-blended. Liquid ingredients used inthe drying-type joint compound of the invention can include water,latex, glycol, dibutyl pthalate, preservatives, defoamers, andhumectants. For example, water and latex (e.g., in the form of anemulsion) can be pre-blended, while the remaining liquid ingredients(described in detail below) can be separately pre-blended.Alternatively, all liquid ingredients can be pre-blended together.

Some ingredients, such as thickeners and polymeric set retarders usefulin the invention, are available in either liquid form or powder form.

Generally, fillers and extenders can also be used in a drying-type jointcompound of the invention. Suitable fillers include perlite, gypsum(calcium sulfate dihydrate), mica, and talc. Fillers are generally usedto control the density of the joint compound, and may also provide otheradvantageous properties to a joint compound of the invention.

Perlite is preferably used in a drying-type joint compound of theinvention to control the density, shrinkage, and crack resistance of thejoint compound. An expanded perlite, such as SLCEL 43-34 expandedperlite, available from Silbrico Corp. of Chicago, Ill. is preferred.The amount of perlite used is preferably in a range of about 1 weightpercent to about 6 wt. %, based on the total weight of joint compound.However, perlite need not be used in conventional weight joint compoundsof the invention.

Mica is also preferably included in a drying-type joint compound of theinvention. Mica, which is a low bulk density mineral used as a filler orextender, may be purchased from KGM Corp. of Kings Mountain, N.C. Micamay also improve crack resistance of the joint compound. The amount ofmica used is preferably in a range of about 1 wt. % to about 4 wt. %,based on the total weight of joint compound.

Some embodiments of the inventive drying-type joint compound, inaddition to limestone, also include gypsum (calcium sulfate dihydrate).The amount of gypsum used in the joint compound is preferably in a rangeof about 5 wt. % to about 60 wt. % (based on the total weight of jointcompound).

Talc is preferably included in a drying-type joint compound of theinvention to enhance application properties and also as a white extenderpigment. Talc, such as the TALEROM or MP 45-26 products manufactured byBarretts Minerals Inc., of Dillon, Mont., may be used in the jointcompound. The amount of talc used in the joint compound is preferably ina range of about 1 wt. % to about 4 wt. %, based on the total weight ofjoint compound.

Clay is preferably used in a drying-type joint compound of the inventionas a non-leveling agent and/or a thickening agent that controls theviscosity or rheology of the final product. Clay also helps enhance orcreate the water-holding properties of the joint compound. A clay suchas SUPERGEL B/Mil White clay available from Mil White of Houston, Tex.,can be used. The amount of clay used is preferably in a range of about 1wt. % to about 4 wt. %, based on the total weight of joint compound.

Thickeners are used to control the viscosity, affect the rheology, andaffect the water holding characteristics of a joint compound. Suitablethickeners can include the METHOCEL HPMC-40320 product manufactured byDow Chemical of Midland, Mich., and products sold under the trade namesHEC Nexton-IPSA, IP8A, and 3082R by Aqualon Chemical Company ofWilmington, Del., a division of Hercules Chemical. The amount ofthickener used in a drying-type joint compound of the invention ispreferably in a range of about 0.1 wt. % to about 5 wt. %, based on thetotal weight of joint compound. More specifically, the amount of aMETHOCEL product used in the joint compound is preferably about 0.1 wt.% to about 1 wt. %, based on weight of joint compound. The amount of aHEC, IP5A, IP8A, and 3082R thickener used in the joint compound may bein a range of about 0.1 wt. % to about 5 wt. %, based on the totalweight of joint compound.

Binders are preferably used in a drying-type joint compound of theinvention to improve bonding to the substrate such as wallboard.Suitable binders can include polyvinyl alcohol, available from AirProducts of Allentown, Pa. A binder is preferably included in a range ofabout 0.1 wt. % to about 0.4 wt. %, based on the total weight of jointcompound.

A glycol can be used in a joint compound to provide functionalproperties to the joint compound such as wet edge, open time,controlling drying time, and freeze/thaw stability. Glycols, such asdiethyl glycol, manufactured by Dow Chemical Co. of Midland, Mich., andethylene glycol and propylene glycol are preferred. The amount of glycolused in a drying-type joint compound of the invention is preferably in arange of about 0.1 wt. % to about 1 wt. %, based on total weight ofjoint compound.

Latex, such as Air Flex 530BP manufactured by Air Product of Allentown,Pennsylvania, and Reichhold 40716 manufactured by Reichhold Corp. ofRaleigh, N.C., can be used in the joint compound. Additional latexesthat can be used include ethylene vinyl acetate, polyvinyl acetateemulsion, and vinyl acetate acrylate latex. The amount of latex used ina drying-type joint compound is preferably in a range of about 2 wt. %to about 2.9 wt. %, based on total weight of joint compound.

A defoamer, such as the NXZ 9201A defoamer manufactured by Geo Chemicalof Clasterd, N.J., can be included in a drying-type joint compound ofthe invention, preferably in a range of about 0.1 18 wt. % to about0.125 wt. %, based on total weight of joint compound. Generally, anyhydrocarbon-based or silicon-based defoamer may be used.

A humectant, such as sorbitol available from Rogette Corp. of Gurnee,Ill. can be included in a drying-type joint compound of the invention,preferably in a range of about 0.01 wt. % to about 0.05 wt. %, based ontotal weight of joint compound.

The drying-type joint compound of the invention is a multi-purpose jointcompound, useful both in applications where a conventional drying-typejoint compound would be used, and in combination with a setting-typejoint compound to create a hybrid joint compound useful in a variety ofapplications, both where setting-type joint compounds are useful andwhere drying-type joint compounds are useful.

The drying-type joint compound of the invention, when combined with acalcium sulfate hemihydrate-based, setting-type joint compound andwater, produces a hybrid joint compound that has advantages of bothindividual types of joint compounds (such as good strength and ease ofsanding), yet sets and/or dries in a time frame acceptable for practicaland commercial use.

For example, whereas a drying-type joint compound of the prior art, whencombined with a conventional setting-type joint compound (having asetting time of about 210 minutes) in a ratio of 2:1 by volume(drying:setting) would dry and/or set in as little as 60 minutes, ahybrid joint compound of the invention made with the same conventionalsetting-type joint compound (having a setting time of about 210 minutes)preferably sets and/or dries in about 80 to about 150 minutes, mostpreferably about 130 minutes.

The drying-type joint compound of the invention can also be used as ifit were a conventional drying-type joint compound, the polymeric setretarding composition used in the joint compound of the invention havingno deleterious effects on the joint compound's performance when usedalone.

Thus, another aspect of the invention is a hybrid joint compoundincluding a water-soluble polymeric set retarder formed from a monomerhaving two or more carboxyl groups, water, calcium carbonate, andcalcium sulfate hemihydrate. Preferably, the hybrid joint compoundincludes at least about 10 wt. % calcium carbonate. Preferably, thehybrid joint compound includes at least about 10 wt. % calcium sulfatehemihydrate.

Water-soluble polymeric set retarders useful and preferred in a hybridjoint compound of the invention are those described above in relation tothe drying-type joint compound of the invention.

When used in a hybrid joint compound, the amount of the water-solublepolymeric set retarder can vary depending upon the setting time of theparticular setting-type joint compound used, the relative amounts ofeach type of joint compound used, and the setting time desired for thehybrid joint compound.

Another aspect of the invention is a method of forming a hybriddrying-type/setting-type joint compound including the steps of forming afirst mixture of water, a water-soluble polymeric set retarder formedfrom a monomer having two or more carboxyl groups, and calciumcarbonate, forming a second mixture of calcium sulfate hemihydrate andwater, and combining the first and second mixtures.

The first mixture of water, a water-soluble polymeric set retarderformed from a monomer having two or more carboxyl groups, and calciumcarbonate preferably includes at least about 10 wt. % calcium carbonatebased upon the weight of the entire first mixture. This mixture alsopreferably includes the preferred optional ingredients recited above inrelation to the drying-type joint compound of the invention, in thepreferred ranges recited. Moreover, this mixture can contain theadditional optional ingredients recited above in relation to thedrying-type joint compound of the invention, in the preferred rangesrecited. This mixture can also contain additional optional ingredientssuitable for use in joint compounds that do not otherwise interfere withthe set time.

The second mixture of calcium sulfate hemihydrate and water preferablyincludes at least about 10 wt. %, more preferably at least about 30 wt.%, most preferably at least about 90 wt. % calcium sulfate hemihydrate,based upon the weight of the entire mixture. This mixture alsopreferably includes talc and a suitable set retarder. This secondmixture can optionally include mica, latex, methylcellulose, afungicide, a defoamer, a stabilizer, and other additives useful insetting-type joint compounds.

Preferably, the first mixture is combined with the second mixture in aratio of 2:1 by volume (drying:setting).

EXAMPLES

The following examples are provided to illustrate the invention but arenot intended to limit the scope of the invention.

Example 1

A compound useful as a water-soluble polymeric set retarder in thedrying-type joint compound of the invention, ALCOSPERSE 408 terpolymer,was added in various amounts to a conventional all-purpose, drying-typejoint compound (GOLD BOND all-purpose joint compound, sold by NationalGypsum Company). The drying-type joint compound with polymeric setretarder was allowed to stand for various amounts of time, from 4 daysto 6 months. Next, an amount of a conventional setting-type calciumsulfate hemihydrate-containing dry powder joint compound (STA SMOOTH(210), sold by National Gypsum Company) equivalent to one part by volumewas weighed and placed into a container, followed by the addition of twoparts by volume of the GOLD BOND all-purpose joint compound withpolymeric set retarder, and a small amount of water, and the componentswere mixed. The various volumes were correlated, approximately, withweights. Approximate set time was measured for each composition.Compositions and set times are tabulated below.

TABLE 2 STA GOLD ALCOSPERSE 408 SMOOTH BOND (% of total weight of timeelapsed approximate 210 AP water GOLD BOND AP) before mixing set time33.0 g 186.5 g 5.6 g 0.03 4 days  80 min 33.0 g 186.5 g 5.1 g 0.05 4days 150 min 33.0 g 186.5 g 5.0 g 0.05 10 days 135 min 33.0 g 186.5 g5.0 g 0.05 21 days 145 min 33.0 g 186.5 g 5.0 g 0.05 6 months 140 min

The results show that a drying-type joint compound of the invention isstorage stable (i.e., does not lose its set retarding potency towardscalcium sulfate hemihydrate) for at least 6 months.

Comparative Example 2

Compositions consisting of GOLD BOND all purpose drying-type jointcompound and one of two different sodium polyacrylate copolymers wereprepared. The sodium polyacrylate copolymers used are sold under thetrade names RHODOLINE 231 (acrylamide-acrylic acid copolymer sodiumsalt) and RHODOLINE A77 (proprietary formulation), by Rhodia Inc.,Cranbury, N.J. Each composition contained 373.0 g of GOLD BOND allpurpose drying-type joint compound and 0.007 wt. % to 0.1 wt. % (basedon the weight of drying type joint compound) of either RHODOLINE 231sodium polyacrylate copolymer or RHODOLINE A77 sodium polyacrylatecopolymer.

The drying-type joint compound with sodium polyacrylate copolymer waseither immediately combined with a setting-type joint compound andwater, or allowed to stand for various amounts of time.

Two parts by volume of the drying-type joint compound with additive thusmade were added to one part by volume (66.0 g) of STA SMOOTH 210setting-type joint compound and 5.0 g of water, and mixed.

When the drying-type joint compound with sodium polyacrylate copolymeradditive was immediately mixed with the STA SMOOTH 210 setting-typejoint compound and water, set times were increased to about 3 to 4 hours(with 0.01 wt. % additive) and to over 4 days (with 0. 1 wt. %additive), compared to 75 minutes using no additive. Specifically, theset time was increased to 160 minutes when using 0.007 wt. % RHODOLINEA77 sodium polyacrylate copolymer.

However, when the drying-type joint compound with either sodiumpolyacrylate copolymer was allowed to stand, the additive lost itsretarding potency fairly rapidly—in as little time as within a twentyfour hour period—and was completely ineffective at 21 days standingtime. Specifically, the set time after 21 days was 80 minutes using0.007 wt. % RHODOLINE A77 sodium polyacrylate copolymer.

The foregoing description is given for clearness of understanding only,and no unnecessary limitations should be understood therefrom, asmodifications within the scope of the invention may be apparent to thosehaving ordinary skill in the art.

What is claimed is:
 1. A joint compound, comprising about 20 wt. % toabout 37 wt. % of water; at least about 50 wt. % of calcium carbonate;and about 0.001 wt. % to about 0.5 wt. % of a water-soluble polymericset retarder formed from a monomer having at least two moieties bound tosuccessive carbon atoms, wherein the successive carbon atoms form atleast part of the polymeric backbone of the polymeric set retarder, andwherein the at least two moieties each contain at least one carboxylgroup.
 2. The joint compound of claim 1, wherein the monomer is anunsaturated dicarboxylic acid or a derivative of an unsaturateddicarboxylic acid.
 3. The joint compound of claim 1, wherein the monomeris selected from the group consisting of maleic acid, derivatives ofmaleic acid, and mixtures thereof.
 4. The joint compound of claim 1,wherein the polymeric set retarder has a weight average molecular weightof about 1,000 to about 15,000.
 5. The joint compound of claim 1,wherein the polymeric set retarder is a homopolymer or a copolymer. 6.The joint compound of claim 1, wherein the polymeric set retarder is aterpolymer formed from: maleic acid; acrylic acid; and a nonionic oranionic monomer.
 7. The joint compound of claim 1, comprising about 0.01wt. % to about 0.1 wt. % polymeric set retarder.
 8. The joint compoundof claim 1, comprising at least about 60 wt. % calcium carbonate.
 9. Ajoint compound consisting essentially of about 20 wt. % to about 37 wt.% of water; at least about 50 wt. % of calcium carbonate; and about0.001 wt. % to about 0.5 wt. % of a water-soluble polymeric set retarderformed from a monomer having at least two moieties bound to successivecarbon atoms, wherein the successive carbon atoms form at least part ofthe polymer backbone of the polymeric set retarder, and wherein the atleast two moieties each contain at least one carboxyl group.
 10. Thejoint compound of claim 9, wherein the polymeric set retarder has aweight average molecular weight of about 1,000 to about 15,000.
 11. Thejoint compound of claim 9, wherein the polymeric set retarder is ahomopolymer, copolymer, or terpolymer.
 12. The joint compound of claim9, comprising about 0.01 wt. % to about 0.1 wt. % polymeric setretarder.
 13. The joint compound of claim 9, comprising at least about60 wt. % calcium carbonate.
 14. A joint compound consisting of about 20wt. % to about 37 wt. % of water; at least about 50 wt. % of calciumcarbonate; and about 0.001 wt. % to about 0.5 wt. % of a water-solublepolymeric set retarder formed from a monomer having at least twomoieties bound to successive carbon atoms, wherein the successive carbonatoms form at least a part of the polymer backbone of the polymeric setretarder, and wherein the at least two moieties each contain at leastone carboxyl group.
 15. A method of producing a joint compound, themethod comprising combining a water-soluble polymeric set retarderformed from a monomer having at least two moieties on at least twosuccessive carbon atoms, water, and calcium carbonate to form a stable,drying-type/setting-type hybrid composition; wherein the at least twomoieties each contain at least one carboxyl group and the at least twosuccessive carbon atoms form at least a part of the polymer backbone-ofthe polymeric set retarder.
 16. The method of claim 15, herein themonomer is an unsaturated dicarboxylic acid or a derivative of anunsaturated dicarboxylic acid.
 17. The method of claim 15, wherein themonomer is selected from the group consisting of maleic acid,derivatives of maleic acid, and mixtures thereof.
 18. The method ofclaim 15, wherein the polymeric set retarder has a weight averagemolecular weight of about 1,000 to about 15,000.
 19. The method of claim15, wherein the polymeric set retarder is a homopolymer, a copolymer ora terpolymer.
 20. The method of claim 15, wherein about 10 wt. % toabout 90 wt. % of the polymeric set retarder is formed from the monomerhaving at least two carboxyl groups.
 21. The method of claim 15, whereinthe polymeric set retarder is a terpolymer formed from: maleic acid;acrylic acid; and a nonionic or anionic monomer.
 22. The method of claim15, wherein the mixture comprises about 0.001 wt. % to about 0.5 wt. %polymeric set retarder.
 23. The method of claim 15, wherein the mixturecomprises at least about 50 wt. % calcium carbonate.